1. Field of the Invention
The present invention relates to a laser processing head which laser cuts or welds a workpiece by condensing and applying a laser beam and injecting cutting gas to the workpiece, and a method of operation therefor.
2. Description of the Background Art
FIG. 5 is a sectional view of a conventional laser cutting head shown in Japanese Patent Unexamined Publication No. Sho. 63-273588. In this drawing, the numeral 1 indicates a laser beam, 2 denotes a cutting lens for condensing the laser beam optically, and 3 represents a moveable holder which holds the cutting lens 2. The holder 3 is inserted within the external cylinder 4 and is moveable in both directions coextensive with the in the axis of the laser beam 1. Teeth 3a are formed in a side face of the holder to engage with a worm gear 6. A motor 5 drives the moving holder 3 via a worm mechanism, consisting of the worm gear 6 and the teeth 3a. The motor 5 and worm mechanism constitute a drive section acting to drive the moving holder 3. A sealant 7, which serves as a seal for cutting gas 9, also serves as a guide for the moving holder 3. A nozzle 8, which includes a nozzle end 8a, applies a laser beam to a workpiece 10 after it is condensed by the cutting lens 2. Nozzle 8 also includes a cutting gas supply port 8b to receive the cutting gas 9 for injection onto the workpiece 10. 2a and 2b indicate positions of the cutting lens 2 in a movable range, and the corresponding focal points of the laser beam 1 are indicated by 11a and 11b. Typically, the volume defined by the cylinder 4 in the laser source direction is open to atmospheric pressure.
The operation of the laser cutting head will now be described in accordance with FIG. 5. The laser beam 1 is condensed optically by the cutting lens 2 and applied to the workpiece 10. The cutting gas 9, which is generally dry air in the case of aluminum cutting, is injected onto the workpiece 10 from the front end 8a of the nozzle 8 on the same axis as the condensed laser beam 1.
The cutting sequence of the laser cutting head will now be described. When the cutting lens 2 is located at position 2a, the corresponding focal point 11a is located at the surface of the workpiece 10, and the workpiece 10 is pierced at a cutting start point. When a hole is made, the motor 5 is driven under the control of a control signal from a numerical control apparatus, not shown, to move the moving holder 3 toward the workpiece 10 via the worm gear 6. The cutting lens 2 moves to position 2b and the corresponding focal point 11b is located at the bottom of the workpiece 10.
At this focal point 11b, laser cutting is performed with respect to the hole pierced. Since cutting gas pressure at this time must be large enough to blow the metal fused by laser energy toward the bottom surface of the workpiece 10, the internal gas pressure of the nozzle 8 is set to an extremely high pressure, e.g., in a range between 5 kgG/cm.sup.2 and 9 kgG/cm.sup.2.
Hence, high cutting gas pressure is applied to portions A of the lens and lens holder, marked with arrows (.uparw.) in the drawing. For example, if the cutting lens is 50 mm in diameter and the cutting gas pressure applied is 8 kgG/cm.sup.2, the thrust which presses the moving holder 3 toward the laser beam 1 application side (top side in the drawing) by means of the cutting gas pressure is approximately 300 kgf because the outside diameter of the moving holder 3 holding the cutting lens 2 is approximately 70 mm. Clearly, the motor 5, the worm gear 6 and other parts constituting the drive section for driving the moving holder 3 must be designed to resist a greater force or thrust.
In the conventional laser cutting head arranged as described above, the nozzle side end portions of the cutting lens and the moving holder that supports the cutting lens encounter a comparatively large force that results from the cutting gas that is supplied through the cutting gas supply port and flows within the nozzle for injection onto the workpiece from the nozzle tip. By contrast, the opposite end of the holder and lens is open to ambient air pressure. As a result, the drive means consisting of the motor, the worm gear and other parts for reciprocating the moving holder in the direction of the laser beam must be relatively large in size.